Often, in small vessels, repair work is carried out by the owner and in many cases the owners are not qualified engine fitters or electricians. Consequently, repairs and maintenance are not always carried out in a professional manner and are not recorded in a maintenance record book. The mechanic did not know what the wires were for and did not verify their use with the owner before reconnecting them, but the wiring from the discontinued lighting system should have been removed in its entirety once it became redundant. Both the removal and the priming of the fuel system allowed gasoline to drain into the engine compartment bilge. This was not taken into account by either the mechanic or the owner and no means of checking the bilge or ventilating it was used during or after the repairs. The propane bottle for the galley stove was stowed inside the galley/wheel-house instead of in its normal position on deck. The bottle's shut-off valve was closed and, even though the flexible hose was damaged, no propane leaked to add fuel to the fire.Analysis Often, in small vessels, repair work is carried out by the owner and in many cases the owners are not qualified engine fitters or electricians. Consequently, repairs and maintenance are not always carried out in a professional manner and are not recorded in a maintenance record book. The mechanic did not know what the wires were for and did not verify their use with the owner before reconnecting them, but the wiring from the discontinued lighting system should have been removed in its entirety once it became redundant. Both the removal and the priming of the fuel system allowed gasoline to drain into the engine compartment bilge. This was not taken into account by either the mechanic or the owner and no means of checking the bilge or ventilating it was used during or after the repairs. The propane bottle for the galley stove was stowed inside the galley/wheel-house instead of in its normal position on deck. The bottle's shut-off valve was closed and, even though the flexible hose was damaged, no propane leaked to add fuel to the fire. A length of two-core electrical wire from a redundant circuit was left in the engine compartment bilge. A mechanic retained to complete work on the main engine inadvertently reconnected the redundant wire to the starter batteries. A closed circuit was caused by the bare cropped end of the redundant wire being in sea water in the bilge. Gasoline had been spilled in the engine compartment bilge when the fuel supply pipe between the fuel lift pump and the carburettor was removed, and when the system was primed. No measures were taken by those involved in the repair to monitor gasoline fumes or remove gasoline from the bilge. The redundant electrical wire overheated, burnt off its insulation and ignited the gasoline fumes and the gasoline on top of the water in the bilge. The accompanying explosion increased the severity and extent of the fire. The raised wheel-house floorboards effectively cut off access to the after door for the two persons sitting in the forward seats.Findings A length of two-core electrical wire from a redundant circuit was left in the engine compartment bilge. A mechanic retained to complete work on the main engine inadvertently reconnected the redundant wire to the starter batteries. A closed circuit was caused by the bare cropped end of the redundant wire being in sea water in the bilge. Gasoline had been spilled in the engine compartment bilge when the fuel supply pipe between the fuel lift pump and the carburettor was removed, and when the system was primed. No measures were taken by those involved in the repair to monitor gasoline fumes or remove gasoline from the bilge. The redundant electrical wire overheated, burnt off its insulation and ignited the gasoline fumes and the gasoline on top of the water in the bilge. The accompanying explosion increased the severity and extent of the fire. The raised wheel-house floorboards effectively cut off access to the after door for the two persons sitting in the forward seats. Gasoline fumes and gasoline that had been spilt in the engine compartment bilges ignited when defunct electrical wiring, which had been inadvertently connected to the starter batteries, overheated after short circuiting in sea water in the bilge. The ensuing explosion resulted in extensive fire damage in the wheel-house.Causes and Contributing Factors Gasoline fumes and gasoline that had been spilt in the engine compartment bilges ignited when defunct electrical wiring, which had been inadvertently connected to the starter batteries, overheated after short circuiting in sea water in the bilge. The ensuing explosion resulted in extensive fire damage in the wheel-house.